1. Field of the Invention
This invention relates to purification systems for wastes, and more particularly to purification systems for agricultural and livestock waste that utilize photosynthetic microorganisms in a photobioreactor to biodegrade and remove organic and inorganic matter.
2. Description of the Related Art
Over the past few decades, there has been an exponential increase in the human population accompanied by a concomitant increase in the demand for cattle, poultry, fish and other livestock and agricultural products. However, the increased demand for agricultural and livestock products necessarily results in an increased amount of agricultural and livestock waste. In addition, the rise in industrial farming, wherein livestock are concentrated in small areas to increase the efficiency of growth, has resulted in extremely high concentrations of waste in localized areas which exacerbates pollution problems immensely. Combined with municipal waste from the increasing human population, the disposal of large amounts of waste products presents a significant problem. For example, in Japan about seven million tons of agricultural waste and three million tons of animal waste are discharged each year. Similarly high discharges are encountered in the USA and Europe. See, for example, xe2x80x9cAnimal Waste Pollution in America: An Emerging National Problem; Environmental Risks of Livestock and Poultry Productionxe2x80x9d, Senate Committee on Agriculture, Nutrition, and Forestry (December, 1997), which discusses the health, environmental, and economic problems of animal wastes in the United States. Accordingly, there is an urgent need to address pollution problems arising from increased levels of agriculture and livestock.
Several methods to process xe2x80x9chigh strengthxe2x80x9d wastes generated by livestock and using photosynthetic organisms are known. For example, U.S. Pat. No. 3,955,318 discloses a system for treating sewage or cannery waste using unicellular algae. This system uses an algae/aerobic bacteria consortium to treat waste. However, high strength agricultural waste containing significant levels of total organic carbon (TOC) and biological oxygen demand (BOD) are not processable by this method due to the narrow culture conditions of the algae.
U.S. Pat. No. 4,267,038 discloses a system in which wastewater is treated in an anaerobic digester tank complex to reduced organic wastes, followed by treatment by an algae culture. However, the anaerobic digester treatment step is generally insufficient to remove enough contaminants from the waste stream and results in slow growth or death of the algae culture.
U.S. Pat. Nos. 4,348,285 and 4,432,869 disclose methods of treating liquid agricultural waste using (1) treatment using a combination of algae and bacteria culture, followed by (2) treatment using a rotifer culture to consume the algae/bacteria. However, most algae have a lower tolerance to raw, high strength wastes as compared to bacteria. As a result, exposure of algae to raw, high strength agricultural wastes generally results in death of the algae. Accordingly, this method is inefficient due to loss of the algae culture during use.
U.S. Pat. No. 5,795,480 discloses a method for treating wastes using heterotrophic bacteria in a first step, then treating the effluent using immobilized photosynthetic bacteria, and finally treating the effluent with photosynthetic and heterotrophic bacteria with activated sludge. However, this process does not utilize algae.
Accordingly, what is needed in the art is an efficient and cost-effective method of processing agricultural and livestock wastes that utilizes photosynthetic organisms and that preferably produces commercially valuable by-products. The present invention is believed to be an answer to that need.
In one aspect, the present invention is directed to a method for treating a waste stream containing organic and inorganic wastes, comprising the steps of: (a) contacting a waste stream comprising organic and inorganic wastes with a first mixture of microorganisms comprising one or more photosynthetic prokaryotic organisms under controlled process conditions and in the presence of light in at least one first reaction vessel, the first reaction vessel in fluid communication with at least one first photobioreactor, wherein a first portion of the wastes is assimilated by the first mixture of microorganisms to produce a partially purified waste stream comprising the first mixture of microorganisms and a second portion of the wastes; (b) removing the first mixture of microorganisms from the partially purified waste stream to produce an isolated first mixture of microorganisms and a partially purified effluent stream containing the second portion of the organic waste; (c) transferring the partially purified effluent stream from the at least one first reaction vessel to at least one second reaction vessel; (d) contacting the partially purified effluent stream with a second mixture of microorganisms comprising algae under controlled process conditions and in the presence of light in the at least one second reaction vessel, the second reaction vessel in fluid communication with at least one second photobioreactor, wherein substantially all of the second portion of the organic wastes are assimilated by the second mixture of microorganisms to produce a substantially purified waste stream comprising the second mixture of microorganisms and a substantially purified effluent; and (e) removing the second mixture of microorganisms from the substantially purified waste stream to produce an isolated second mixture of microorganisms and a substantially purified effluent stream.
In yet another aspect, the present invention is directed to a method for treating a waste stream containing organic and inorganic wastes, comprising the steps of: (a) contacting a waste stream comprising organic and inorganic wastes with a first mixture of microorganisms comprising one or more photosynthetic prokaryotic organisms under controlled process conditions and in the presence of light in at least one first photobioreactor, wherein a first portion of the wastes is assimilated by the first mixture of microorganisms to produce a partially purified waste stream comprising the first mixture of microorganisms and a second portion of the wastes; (b) removing the first mixture of microorganisms from the partially purified waste stream to produce an isolated first mixture of microorganisms and a partially purified effluent stream containing the second portion of the organic waste; (c) transferring the partially purified effluent stream from the at least one first photobioreactor to at least one second photobioreactor; (d) contacting the partially purified effluent stream with a second mixture of microorganisms comprising algae under controlled process conditions and in the presence of light in the at least one second photobioreactor, wherein substantially all of the second portion of the organic wastes are assimilated by the second mixture of microorganisms to produce a substantially purified waste stream comprising the second mixture of microorganisms and a substantially purified effluent; and (e) removing the second mixture of microorganisms from the substantially purified waste stream to produce an isolated second mixture of microorganisms and a substantially purified effluent stream.
The photobioreactor utilized in the process of the present invention preferably comprises an upstanding upwardly open structure such as a tank, a substantially transparent tube wound helically on the core structure or tubes in parallel extending from a manifold, wherein the exterior and interior of the tube or tubes are exposed to light; and means to encourage light penetration into the tube in the region of contact between the tube and the core structure. Under certain conditions in which the level of natural, ambient light is low, (e.g., high latitudes or during winter months), addition of a photobioreactor to the present invention can increase the amount of light made available to the photosynthetic microorganisms, and result in improved uptake of waste materials from the waste stream.
These and other aspects will become apparent upon reading the following detailed description of the invention.